Synthesis of cis-1,4-polybutadiene rubber in presence of cobalt containing catalyst system

ABSTRACT

It has been determined that 1,3-butadiene monomer can be polymerized into cis-l,4-polybutadiene rubber utilizing a cobalt-based catalyst system which is comprised of (a) an organocobalt compound, (b) a trialkylaluminum compound and (c) hexafluoro-2-propanol. The use of this catalyst system results in extremely fast rates of polymerization. The molecular weight of the cis-1,4- polybutadiene rubber made utilizing this cobalt-based catalyst system can be regulated by conducting the polymerization in the presence of 1,5-cyclooctadiene. This present invention more specifically discloses a catalyst system which is particularly useful for polymerizing 1,3-butadiene monomer into cis-1,4-polybutadiene, said catalyst system being comprised of (a) an organocobalt compound, (b) a trialkylaluminum compound and (c) hexafluoro-2-propanol. The subject invention further discloses a process for synthesizing cis-1,4-polybutadiene rubber which comprises polymerizing 1,3-butadiene in the presence of (a) an organocobalt compound, (b) a trialkylaluminum compound and (c) hexafluoro-2-propanol.

This is a Divisional of Application Ser. No. 08/692,359, filed on Aug.5, 1996, U.S. Pat. No. 5,733,835.

BACKGROUND OF THE INVENTION

High cis-1,4-polybutadiene rubber typically has a cis-isomer content ofgreater than about 95 percent and is widely used in manufacturing tires.It is widely used in tire tread rubber compounds because it providesimproved treadwear characteristics for automobile and truck tires. Inmost cases, the cis-1,4-polybutadiene rubber is blended with one or moreother rubbers to attain the desired tire tread characteristics.

It is well known that high cis-1,4-polybutadiene can be prepared bypolymerizing 1,3-butadiene monomer with nickel-based catalyst systems.Such nickel-based catalyst systems contain (a) an organonickel compound,(b) an organoaluminum compound and (c) a fluorine containing compound.Such nickel-based catalyst systems and their use in the synthesis ofcis-1,4-polybutadiene is described in detail in U.S. Pat. No. 3,856,764,U.S. Pat. No. 3,910,869 and U.S. Pat. No. 3,962,375.

The cis-1,4-polybutadiene prepared utilizing such nickel-based catalystsystems typically has a high molecular weight. Due to this highmolecular weight, the cis-1,4-polybutadiene is generally oil-extended.However, this precludes the cis-1,4-polybutadiene from being utilized inmany applications. For instance, such oil-extended rubbers cannot beutilized in tire sidewalls which contain white sidewall compounds. Inany case, there is a large demand for cis-1,4-polybutadiene having areduced molecular weight which can be processed without beingoil-extended.

Various compounds have been found to act as molecular weight-reducingagents when used in conjunction with the nickel-based catalyst system.For instance, U.S. Pat. No. 4,383,097 discloses that ethylene andalpha-olefins, such as propylene and butylene, act as molecularweight-reducing agents when utilized in conjunction with suchthree-component nickel catalyst systems. Canadian Patent 1,236,648indicates that 1-butene, isobutylene, cis-2-butene, trans-2-butene andallene act as molecular weight regulators when used in conjunction withsuch nickel-based catalyst systems. U.S. Pat. No. 4,383,097 reveals thatcertain nonconjugated diolefins, such as 1,4-pentadiene, 1,6-heptadieneand 1,5-hexadiene, act as molecular weight-reducing agents when utilizedin conjunction with such catalyst systems. U.S. Pat. No. 5,100,982indicates that cis-1,4-polybutadiene having reduced molecular weight anda broad molecular weight distribution can be synthesized with certainnickel-based catalyst systems in the presence of halogenated phenols,such as para-chlorophenol.

The use of nickel-based catalyst systems results in commercially viablepolymerization rates. However, the development of catalyst systems whichresult in faster polymerization rates would be highly desirable. Thisis, of course, because faster rates of polymerization generally resultin lower production costs. However, it is also critical for there to bea means for controlling the molecular weight of thecis-1,4-polybutadiene rubber made with such a catalyst system.

High cis-1,4-polybutadiene can also be prepared using cobalt-basedcatalyst systems. Typical cobalt catalysis uses a cobalt salt of anorganic acid in conjunction with alkylaluminum chlorides as cocatalysts,and in cases where the chlorine/aluminum ratio is less than or equal to1, water is used as an activator. The cobalt catalyzed polymerizationsfrequently use aromatic solvents, such as benzene and toluene, ormixtures of aromatic and aliphatic solvents. Polymer molecular weight isaffected by solvent, catalyst component concentration, monomerconversion, and reaction temperature. Molecular weight can also becontrolled by the use of transfer agents, such as allene, ethylene,propylene, and hydrogen.

SUMMARY OF THE INVENTION

It has been unexpectedly determined that 1,3-butadiene monomer can bepolymerized into cis-1,4-polybutadiene rubber at a very fastpolymerization rate utilizing a cobalt-based catalyst system which iscomprised of (a) an organocobalt compound, (b) a trialkylaluminumcompound and (c) hexafluoro-2-propanol. In fact, virtually quantitativeyields can be achieved after polymerization times of only about one ortwo minutes. It has further been unexpectedly found that1,5-cyclooctadiene acts as molecular weight-reducing agent when employedin conjunction with the cobalt-based catalyst systems of this invention.

The subject invention more specifically discloses a catalyst systemwhich is particularly useful for polymerizing 1,3-butadiene monomer intocis-1,4-polybutadiene, said catalyst system being comprised of (a) anorganocobalt compound, (b) a trialkylaluminum compound and (c)hexafluoro-2-propanol.

The subject invention further discloses a process for synthesizingcis-1,4-polybutadiene rubber which comprises polymerizing 1,3-butadienein the presence of (a) an organocobalt compound, (b) a trialkylaluminumcompound and (c) hexafluoro-2-propanol.

DETAILED DESCRIPTION OF THE INVENTION

The cobalt catalyst system of this invention can potentially be used topromote solution polymerizations, bulk polymerizations or vapor phasepolymerizations. However, the polymerizations of this invention willtypically be carried out as solution polymerizations in a hydrocarbonsolvent which can be one or more aromatic, paraffinic or cycloparaffiniccompounds. These solvents will normally contain from 4 to about 10carbon atoms per molecule and will be liquids under the conditions ofthe polymerization. Some representative examples of suitable organicsolvents include isooctane, cyclohexane, normal hexane, benzene,toluene, xylene, ethylbenzene and the like, alone or in admixture.

In the solution polymerizations of this invention, there will normallybe from about 5 to about 35 weight percent monomers in thepolymerization medium. Such polymerization media are, of course,comprised of the organic solvent and the 1,3-butadiene monomer. As thepolymerization proceeds, monomer is converted to polymer and,accordingly, the polymerization medium will contain from about 5 toabout 35 weight percent unreacted monomers and polymer. In most cases,it will be preferred for the polymerization medium to contain from about10 to about 30 weight percent monomers and polymers. It is generallymore preferred for the polymerization medium to contain from 20 to 25weight percent monomers and polymers.

Polymerization is typically started by adding the cobalt-based catalystsystem to the polymerization medium. In cases where it is desirable tomoderate the molecular weight of the polymer being produced,1,5-cyclooctadiene will additionally be added as a molecular weightregulator. The catalyst components (the organocobalt compound, thetrialkylaluminum compound and the hexafluoro-2-propanol) will typicallybe added to the polymerization medium as separate components. Thecatalyst components can be added to the polymerization mediumsimultaneously or sequentially because the order of addition of catalystcomponents is not critical. However, it is typically preferred tosequentially add the trialkylaluminum compound followed by the additionof the organocobalt compound, with the hexafluoro-2-propanol being addedlast. In batch techniques, it is normally convenient to add the catalystcomponents and optionally the 1,5-cyclooctadiene to a polymerizationmedium which already contains 1,3-butadiene monomer in an organicsolvent. In order to facilitate charging the catalyst components intothe reaction zone "in situ," they can be dissolved in a small amount ofan inert organic solvent or butadiene monomer.

The organocobalt compounds utilized in the catalyst systems of thisinvention are typically cobalt salts of organic acids which contain from1 to about 20 carbon atoms. Some representative examples of suitableorganocobalt compounds include cobaltous benzoate, cobalt acetate,cobalt naphthenate, cobalt octanoate, cobalt stearate, and cobalticacetylacetonate. Cobalt naphthenate and cobalt octoate are highlypreferred organocobalt compounds. Cobalt 2-ethylhexanoate, which iscommonly referred to as cobalt octanoate (CoOct), is the organocobaltcompound which is most commonly used due to economic factors.

The trialkylaluminum compounds that can be utilized have the structuralformula: ##STR1## in which R₁, R₂ and R₃ represent alkyl groups(including cycloalkyl groups) which contain from 1 to about 20 carbonatoms. It is preferred for R₁, R₂ and R₃ to represent alkyl groups whichcontain from 1 to about 10 carbon atoms. It is more preferred for R₁, R₂and R₃ to represent alkyl groups which contain from 2 to about 5 carbonatoms.

Some representative examples of trialkylaluminum compounds that can beutilized include trimethyl aluminum, triethyl aluminum, tri-n-propylaluminum, triisopropyl aluminum, tri-n-butyl aluminum, triisobutylaluminum, tripentyl aluminum, trihexyl aluminum, tricyclohexyl aluminumand trioctyl aluminum. The preferred trialkylaluminum compounds includetriethyl aluminum (TEAL), tri-n-propyl aluminum, triisobutyl aluminum(TIBAL) and trihexyl aluminum.

The hexafluoro-2-propanol which is used in the catalyst systems of thisinvention is 1,1,1,3,3,3-hexafluoro-2-propanol which is of the formula:(CF₃)₂ CHOH. Hexafluoro-2-propanol is also known as hexafluoroisopropylalcohol.

The three-component cobalt catalyst systems utilized in the practice ofthe present invention have activity over a wide range of catalystconcentrations and catalyst component ratios. The three catalystcomponents interact to form the active catalyst system. As a result, theoptimum concentration for any one component is very dependent upon theconcentrations of each of the other two catalyst components.Furthermore, while polymerization will occur over a wide range ofcatalyst concentrations and ratios, the most desirable properties forthe polymer being synthesized are obtained over a relatively narrowrange.

Polymerizations will typically be carried out utilizing a mole ratio ofthe trialkylaluminum compound to the organocobalt compound which iswithin the range of about 5:1 to about 50:1. It is preferred for themolar ratio of the trialkylaluminum compound to the organocobaltcompound to be within the range of about 10:1 to about 30:1. It is morepreferred for the molar ratio of the trialkylaluminum compound to theorganocobalt compound to be within the range of about 15:1 to about25:1.

The molar ratio of the hexafluoro-2-propanol to the trialkylaluminumcompound will typically be within the range of about 1:1 to about 3:1.It is normally preferred for the molar ratio of thehexafluoro-2-propanol to the trialkylaluminum compound to be within therange of about 1.2:1 to about 2:1. It is generally more preferred forthe molar ratio of the hexafluoro-2-propanol to the trialkylaluminumcompound to be within the range of about 1.3:1 to about 1.7:1.

The concentration of the catalyst system utilized in the reaction zonedepends upon factors such as purity, the reaction rate desired, thepolymerization temperature utilized, the reactor design and otherfactors. However, the catalyst system will normally be present in anamount whereby from about 0.0025 phm (parts by weight per 100 parts byweight of monomer) to about 0.018 phm of the organocobalt compound ispresent. In most cases, it is preferred for about 0.0035 phm to about0.0095 phm of the organocobalt compound to be present. It is normallymost preferred for about 0.0065 phm to about 0.0075 phm of theorganocobalt compound to be present.

The amount of 1,5-cyclooctadiene that needs to be employed as amolecular weight-reducing agent varies with the catalyst system, withthe polymerization temperature and with the desired molecular weight ofthe high cis-1,4-polybutadiene rubber being synthesized. For instance,if a high molecular weight rubber is desired, then a relatively smallamount of 1,5-cyclooctadiene is required. On the other hand, in order toreduce molecular weights substantially, a relatively larger amount of1,5-cyclooctadiene will need to be employed. However, as a general rule,from about 0.1 phm (parts by weight per hundred parts of monomer) toabout 1.5 phm of the 1,5-cyclooctadiene will be employed as a molecularweight-reducing agent. It is normally preferred for about 0.35 phm toabout 0.85 phm of the 1,5-cyclooctadiene to be present during thepolymerization. In typical cases where high cis-1,4-polybutadiene rubberhaving a Mooney ML1+4 viscosity of about 55 to about 80 is beingsynthesized, the amount of 1,5-cyclooctadiene utilized will normally bewithin the range of about 0.5 phm to about 0.7 phm.

The temperatures utilized in the polymerizations of this invention arenot critical and may vary from extremely low temperatures to very hightemperatures. For instance, such polymerizations can be conducted at anytemperature within the range of about -10° C. to about 130° C. Thepolymerizations of this invention will preferably be conducted at atemperature within the range of about 20° C. to about 100° C. It isnormally preferred for the polymerization to be carried out at atemperaturew which is within the range of about 65° C. to about 85° C.

Such polymerizations will normally be conducted for a period of timewhich is sufficient to attain a high yield which is normally in excessof about 70 percent and preferably in excess of about 80 percent. Thepolymerization time required to attain such high conversions isextremely short. In fact, conversions in excess of 80 percent can berealized in less than 4 minutes. In most cases, conversions in excess of80 percent can be attained in less than 2 minutes of polymerizationtime. Polymerization times of one minute or less are normally sufficientto attain conversions in excess of 80 percent.

The cis-1,4-polybutadiene rubber made utilizing the techniques of thisinvention typically has a cis content in excess of about 97 percent. Forexample, the cis-1,4-polybutadiene rubber made utilizing the techniquesof this invention will typically have a cis content of about 98 percent,a trans content of about 1 percent and a vinyl content of about 1percent.

After the polymerization is completed, the cis-1,4-polymerization rubbermay be recovered from the resulting polymer solution (rubber cement) byany of several procedures. One such procedure comprises mixing therubber cement with a polar coagulating agent, such as methanol, ethanol,isopropanol, acetone or the like. The coagulated rubber is recoveredfrom the slurry of the polar coagulating agent by centrifugation,decantation or filtration.

Another procedure for recovering the cis-1,4-polybutadiene rubber is bysubjecting the rubber solution to spray drying. Such a procedure isparticularly suitable for continuous operations and has the advantagethat heat requirements are at a minimum. When such a procedure is used,the recovered polymer should be washed soon after recovery with a polarsolvent in order to destroy the remaining active catalyst contained inthe polymer. In such procedures, the vaporized organic solvents are alsoeasily recovered but will normally require purification before beingrecycled.

The practice of this invention is further illustrated by the followingexamples which are intended to be representative rather than restrictiveof the scope of the subject invention. Unless indicated otherwise, allparts and percentages are given by weight. Dilute solutions viscositieswere determined in toluene at 30° C.

EXAMPLES 1-8

In this series of experiments, high cis-1,4-polybutadiene wassynthesized using the catalyst system of this invention. In theprocedure used, a series of 4-ounce (118 ml) polymerization bottles werefilled with 100 ml of 16 weight percent solutions of 1,3-butadiene inhexane solvent. The 1,3-butadiene/hexane premix solutions had beenpassed through a silica gel-packed column under a nitrogen atmosphere.The hexane solvent was a mixture of various hexane isomers.

Polymerization was initiated by injecting solutions of the threecatalyst components and 1,5-cyclooctadiene into each of thepolymerization bottles under a nitrogen atmosphere. The polymerizationbottles were capped with a punctured metal cap fitted with aself-sealing gasket and Teflon liner. All catalyst and modifiersolutions were made in hexane solvent which had been passed through asilica gel column. All of the catalyst component and modifier additionswere made with a syringe which was equipped with a hypodermic needle.

A solution of triisobutylaluminum was added first, followed by theaddition of cobalt octanoate, with a solution of hexafluoro-2-propanolbeing added last. The molar ratio of triisobutylaluminum (TIBA) tocobalt octanoate (CoOct) was 20:1 with 0.0172 phm of the cobaltoctanoate and 1 phm of 1,5-cyclooctadiene being added. The molar ratioof hexafluoro-2-propanol (HFI) to triisobutylaluminum is shown in TableI. However, it should be noted that Example 8 was run as a control withno HFI being added.

The polymerizations were carried out by rotating the polymerizationbottles end-over-end for 90 minutes in a constant temperature water bathwhich was maintained at 65° C. After the 90-minute reaction time, thepolymerization was shortstopped by the addition of 1.0 phm ofisopropanol, 1.0 phm of rosin acid and 1.0 phm of butylatedhydroxytoluene. The high cis-1,4-polybutadiene synthesized was isolatedby vacuum oven drying. Polymer yield, dilute solution viscosity (DSV)and Brookfield viscosity (BFV) are reported in Table I. DSV was measuredas a 0.25 g/dl solution in toluene at 30° C. and BFV was measured on 10weight percent solutions in toluene at room temperature.

                  TABLE I                                                         ______________________________________                                        Example   HFI/TIBA DSV         BFV    Yield                                   ______________________________________                                        1         1.00     1.57 dl/g     700 cps                                                                            68%                                     2         1.25     1.62 dl/g     710 cps                                                                            98%                                     3         1.50     1.61 dl/g     750 cps                                                                            100%                                    4         2.00     1.71 dl/g   1,050 cps                                                                            91%                                     5         2.14     1.76 dl/g   1,120 cps                                                                            93%                                     6         2.25     1.90 dl/g   1,750 cps                                                                            87%                                     7         2.50     2.00 dl/g   2,350 cps                                                                            89%                                     8         --       --          --      0%                                     ______________________________________                                    

Inspection of the results in Table I shows that high catalyst activityis attained at HFI/TIBA ratios of greater than 1:1 and that the polymerviscosity (both DSV and Brookfield viscosity) increase with increasingHFI/TIBA ratios. NMR (nuclear magnetic resonance) analysis of thepolymer synthesized showed it to be 98 percent cis-1,4, 1 percenttrans-1,4 and 1 percent vinyl polybutadiene. The polymer was alsodetermined to have a glass transition temperature (T_(g)) of -106° C.and a melting point (T_(m)) of -8 C., both of which are typical of highcis-1,4-polybutadiene.

EXAMPLES 9-15

In this series of experiments, high cis-1,4-polybutadiene wassynthesized using the catalyst system of this invention in the presenceof varying amounts of 1,5-cyclopentadiene (COD). In the procedure used,a series of 32-ounce (946 ml) polymerization bottles were filled with500 ml of 16 weight percent solutions of 1,3-butadiene in hexanesolvent. The 1,3-butadiene/hexane premix solutions had been passedthrough a silica gel-packed column under a nitrogen atmosphere. Thehexane solvent was a mixture of various hexane isomers.

The desired amount of COD was added to each of the polymerizationbottles first. Then, polymerization was initiated by injecting solutionsof the three catalyst components into each of the polymerizationbottles. A solution of triis butylaluminum was added first followed bythe addition of cobalt octanoate with a solution ofhexafluoro-2-propanol being added last. The molar ratio of cobaltoctanoate to triisobutylaluminum to HFI was approximately 1:20:30 with0.0172 phm of the cobalt octanoate and 0.19 phm of triisobutylaluminumbeing added. The amount of 1,5-cyclooctadiene utilized is shown in TableII.

The polymerizations were carried out by leaving the polymerizationbottles in a constant temperature bath which was maintained at 65° C.for 90 minutes. The Mooney ML1+4 viscosity (at 100° C.), dilute solutionviscosity (DSV) and cold flow of the high cis-1,4-polybutadiene rubbersamples made are reported in Table II.

                  TABLE II                                                        ______________________________________                                        Example COD      ML1 + 4    DSV    Cold Flow                                  ______________________________________                                         9      0.35 phm 127        2.80 dl/g                                                                            --                                         10      0.53 phm 80         2.45 dl/g                                                                            --                                         11      0.71 phm 55         2.10 dl/g                                                                            0.50 mg/min                                12      0.81 phm 47         1.91 dl/g                                                                            0.84 mg/min                                13      0.86 phm 40         1.91 dl/g                                                                            1.14 mg/min                                14      0.88 phm 38         1.98 dl/g                                                                            1.82 mg/min                                15      1.06 phm 24         1.66 dl/g                                                                            5.66 mg/min                                ______________________________________                                    

As can be seen from Table II, COD acts as a molecular weight regulator.The Mooney viscosity and DSV of the high cis-1,4-polybutadiene rubbersynthesized decreases with increasing amounts of COD. Thus, molecularweight decreases with increasing amounts of COD. On the other hand, thecold flow of the high cis-1,4-polybutadiene rubber increases withincreasing levels of COD.

EXAMPLES 16-22

In this series of experiments, the effect of catalyst level on yield andDSV was studied. The polymerization procedure used was essentially thesame as the procedure utilized in Examples 1-8 with catalyst levelsbeing varied.

Polymerization was initiated by injecting solutions of the threecatalyst components and 1,5-cyclooctadiene into each of thepolymerization bottles. A solution of triisobutylaluminum was addedfirst, followed by the addition of cobalt octanoate with a solution ofhexafluoro-2-propanol being added last. The molar ratio of cobaltoctanoate to triisobutylaluminum to HFI was 1:20:30. In each of thepolymerizations conducted in this series of experiments, 0.88 phm of1,5-cyclooctadiene was added. The amount of cobalt octanoate,triisobutylaluminum and HFI utilized is shown in Table III. The polymeryield and DSV attained are also shown in Table III.

                  TABLE III                                                       ______________________________________                                        Example  TIBA.sup.1                                                                              CoOct.sup.2                                                                           HFI.sup.3                                                                             Yield                                                                              DSV.sup.4                             ______________________________________                                        16       0.138     0.0121  0.176   96%  1.92                                  17       0.118     0.0104  0.151   96%  1.91                                  18       0.098     0.0086  0.126   96%  2.08                                  19       0.081     0.0069  0.101   95%  1.94                                  20       0.061     0.0052  0.077   92%  2.15                                  21       0.040     0.0034  0.051   74%  2.10                                  22       0.020     0.0017  0.025    0%  --                                    ______________________________________                                         .sup.1 The level of TIBA is reported in phm.                                  .sup.2 The level of CoOct is reported in phm.                                 .sup.3 The level of HFI is reported in phm.                                   .sup.4 DSV is reported in dl/g.                                          

The results listed in Table III show that high polymerization activityis achieved at CoOct levels of 0.0052 phm or higher. Also, the datashows that the polymer DSV is relatively independent of catalyst level,when run in the presence of 1,5-cyclooctadiene.

EXAMPLES 23-26

In this series of experiments, the effect of 1,5-cycloqctadiene level onpolymer molecular weight was studied. The polymerization procedure usedwas essentially the same as the procedure utilized in Examples 1-8 withCOD levels being varied. However, in this series of experiments, thepolymerizations were carried out in 8-ounce (237 ml) polymerizationbottles with the molar ratio of TIBA to CoOct being 10.4:1 and with themolar ratio of HFI to TIBA being 1.95:1. The CoOct was utilized at alevel of 0.086 phm.

The level of COD utilized is reported in Table IV. Table IV also showsthe DSV, number average molecular weight (M_(n)), weight averagemolecular weight (M_(w)) and M_(w) /M_(n) ratio of thecis-1,4-polybutadiene rubber samples made.

                  TABLE IV                                                        ______________________________________                                        Example                                                                              COD      DSV.sup.1                                                                             M.sub.n M.sub.w M.sub.w /M.sub.n                      ______________________________________                                        23     0.0010   2.94    1.7 × 10.sup.5                                                                  7.1 × 10.sup.5                                                                  4.2                                   24     0.0032   2.52    1.4 × 10.sup.5                                                                  5.2 × 10.sup.5                                                                  3.8                                   25     0.0052   2.31    1.1 × 10.sup.5                                                                  3.9 × 10.sup.5                                                                  3.6                                   26     0.0074   2.01    1.0 × 10.sup.5                                                                  3.4 × 10.sup.5                                                                  3.4                                   ______________________________________                                         .sup.1 Reported in dl/g.                                                 

Table IV shows that COD can be used to change the molecular weightdistribution (M_(w) /M_(n)) of the high cis-1,4-plolybutadiene as wellas to regulate its molecular weight. More specifically, a more narrowmolecular weight distribution can be attained by using higher levels ofCOD.

EXAMPLES 27-31

In this series of experiments, the effect of various potential modifierson yield and DSV was studied. The polymerization procedure used wasessentially the same as the procedure utilized in Examples 1-8 with thepolymerizations being conducted in the presence of 0.0092M modifier,which included 1,5-hexadiene, 1,5-cyclooctadiene, dicyclopentadiene orbutene-1. A control was also run (see Example 27). However, in thisseries of experiments, the polymerizations were carried out with themolar ratio of TIBA to CoOct being 17.7:1 and with the molar ratio ofHFI to TIBA being 1.5:1. The CoOct was utilized at a level of 0.029 phm.

The potential modifiers utilized in each experiment are identified inTable V. Table V also shows the yield and DSV of thecis-1,4-polybutadiene rubber samples made.

                  TABLE V                                                         ______________________________________                                        Example    Modifier      Yield  DSV                                           ______________________________________                                        27         none          100%   5.71 dl/g                                     28         1,5-hexadiene 100%   5.70 dl/g                                     29         1,5-cyclooctadiene                                                                           98%   2.27 dl/g                                     30         dicyclopentadiene                                                                            40%   4.79 dl/g                                     31         butene-1      100%   5.62 dl/g                                     ______________________________________                                    

As can be seen from Table V, of the organic compounds evaluated, only1,5-cyclooctadiene acts as a molecular weight regulator when used inconjunction with the catalyst systems of this invention. The resultswith dicyclopentadiene indicate that it is a poison for thepolymerization and that lower DSV is achieved only as a result of loweryield.

EXAMPLES 32-59

Even though the polymerizations described in Examples 1-31 were carriedout for 90 minutes, the Cooct/TIBA/HFI catalyzed polymerization of1,3-butadiene is sufficiently fast that the bulk of the polymerizationis over within 2 minutes. The polymerization procedure used wasessentially the same as the procedure utilized in Examples 1-8 with themolar ratio of TIBA to CoOct being 17.7:1 and with the molar ratio ofHFI to TIBA being 1.5:1. The COD was utilized at a level of 0.85 phm inExamples 32-55 and at a level of 0.75 phm in Examples 56-59. The amountof CoOct utilized is reported in Table VI. The polymerization time (Pzn.Time) and polymer yield are also reported in Table VI.

                  TABLE VI                                                        ______________________________________                                        Example  CoOct         Pzn. Time  Yield                                       ______________________________________                                        32       0.0012 phm    60 seconds 16%                                         33       0.0012 phm    120 seconds                                                                              18%                                         34       0.0012 phm    240 seconds                                                                              20%                                         35       0.0024 phm    60 seconds 15%                                         36       0.0024 phm    120 seconds                                                                              37%                                         37       0.0024 phm    240 seconds                                                                              42%                                         38       0.0036 phm    60 seconds 41%                                         39       0.0036 phm    120 seconds                                                                              46%                                         40       0.0036 phm    240 seconds                                                                              54%                                         41       0.0048 phm    60 seconds 41%                                         42       0.0048 phm    120 seconds                                                                              53%                                         43       0.0048 phm    250 seconds                                                                              68%                                         44       0.0060 phm    60 seconds 49%                                         45       0.0060 phm    120 seconds                                                                              63%                                         46       0.0060 phm    240 seconds                                                                              68%                                         47       0.0140 phm     5 seconds 29%                                         48       0.0140 phm    10 seconds 69%                                         49       0.0140 phm    15 seconds 82%                                         50       0.0140 phm    20 seconds 85%                                         51       0.0240 phm    15 seconds 83%                                         52       0.0240 phm    30 seconds 84%                                         53       0.0240 phm    60 seconds 86%                                         54       0.0240 phm    150 seconds                                                                              89%                                         55       0.0240 phm    300 seconds                                                                              90%                                         56       0.0039 phm    60 seconds 23%                                         57       0.0074 phm    60 seconds 70%                                         58       0.0074 phm    120 seconds                                                                              89%                                         59       0.0150 phm    60 seconds 96%                                         ______________________________________                                    

Table VI shows that the CoOct/TIBA/HFI catalyst system is extremelyactive for the polymerization of 1,3-butadiene monomer into highcis-1,4-polybutadiene rubber. More specifically, Table VI shows thatconversions of greater than 80 percent can be reached in less than 3minutes. In fact, Examples 51-53 and 59 show that conversions of greaterthan 80 percent can be reached in one minute or less. Example 59 showsthat a conversion of greater than 95 percent can be reached in only oneminute.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made without departing from the scope of the present invention.

What is claimed is:
 1. A process for synthesizing cis-1,4-polybutadienerubber hich comprises polymerizing 1,3-butadiene in the presence of (a)at least one cobalt compound selected from the group consisting oforganocobalt compounds and cobalt complexes of an organic acid, (b) atrialkylaluminum compound and (c) hexafluoro-2-propanol.
 2. A process asspecified in claim 1 wherein said polymerization is conducted at atemperature which is within the range of -10° C. to 130° C.
 3. A processas specified in claim 2 wherein the organocobalt compound or the cobaltcomplex of the organic acid is present in an amount which is within therange of 0.0025 phm to 0.018 phm.
 4. A process as specified in claim 3wherein the cobalt compound is a cobalt salt of an organic acid.
 5. Aprocess as specified in claim 4 wherein the trialkylaluminum compound isof the structural formula: ##STR2## wherein R₁, R₂ and R₃ representalkyl groups containing from 1 to 20 carbon atoms.
 6. A process asspecified in claim 5 wherein the molar ratio of the trialkylaluminumcompound to the cobalt salt of an organic acid is within the range of5:1 to 50:1.
 7. A process as specified in claim 6 wherein the molarratio of the hexafluoro-2-propanol to the trialkylaluminum compound iswithin the range of 1:1 to 3:1.
 8. A process as specified in claim 7wherein the molar ratio of the trialkylaluminum compound to the cobaltsalt organic acid is within the range of 10:1 to 30:1.
 9. A process asspecified in claim 8 wherein the molar ratio of thehexafluoro-2-propanol to the trialkylaluminum compound is within therange of 1.2:1 to 2:1.
 10. A process as specified in claim 9 wherein R₁,R₂ and R₃ represent alkyl groups which contain from 1 to about 10 carbonatoms.
 11. A process as specified in claim 10 wherein the cobalt salt ofan organic acid contains from 1 to 20 carbon atoms.
 12. A process asspecified in claim 1 wherein the cobalt compound is selected from thegroup consisting of cobalt benzoate, cobalt acetate, cobalt naphthenate,cobalt octoate, cobalt stearate and cobalt acetylacetonate.
 13. Aprocess as specified in claim 1 wherein the cobalt compound is selectedfrom the group consisting of cobalt naphthenate, cobalt octoate andcobalt neodecanoate.
 14. A catalyst system as specified in claim 12wherein the molar ratio of the trialylaluminum compound to the cobaltcompound which is within the range of 15: 1 to 25:1.
 15. A process asspecified in claim 14 wherein the molar ratio of thehexafluoro-2-propanol to the trialkylaluminum compound is within therange of 1.3:1 to 1.7:1.
 16. A process as specified in claim 5 whereinR₁, R₂ and R₃ represent alkyl groups which contain from 2 to 5 carbonatoms.
 17. A process as specified in claim 15 wherein the cobaltcompound is cobalt octanoate; and wherein the trialkylaluminum compoundis triisobutylaluminum.